The present application describes a technique of using quantum-entangled particles, e.g. photons, for lithography for etching features on a computer chip that are smaller than the wavelength of light used in the etching process, by some fraction related to the number of entangled particles.
Quantum mechanics tells us that certain unobserved physical systems can have odd behavior. A particle which is decoupled from its environment and which has two possible states will not necessarily be in either of those states, until observed. Putting this in quantum mechanical terms, the particle is simultaneously in a xe2x80x9csuperpositionxe2x80x9d of both of those states. However, this only applies while the particle is in certain conditionsxe2x80x94decoupled from its environment. Any attempt to actually observe the particle couples the particle to its environment, and hence causes the particle to default into one or the other of the eigenstates of the observable operator.
This behavior is part of the superposition principle. The xe2x80x9csuperposition principlexe2x80x9d is illustrated by a famous hypothetical experiment, called the cat paradox. a cat in a box with a vial of poison. The vial containing the poison could equally likely be opened or not opened. If the box/cat/poison is decoupled from its environment, then the cat achieves a state where it is simultaneously dead and not dead. However, any attempt to observe the cat, causes the system to default to dead or alive.
The theory of quantum mechanics predicts that N particles can also exist in such superposition states.
Lithography is a process of etching features on a substrate. Photolithography uses light to etch these features. Each spot can be etched, or not etched, to form a desired feature. In general, it is desirable to make the features as small as possible.
In the prior art, called Classical Optical Interferometric Lithography, a lithographic pattern is etched on a photosensitive material using a combination of phase shifters, substrate rotators, and a Mach-Zehnder or other optical interferometer. The minimum sized feature that can be produced in this fashion is on the order of one-quarter of the optical wavelength [Brueck 98]. The only way to improve on this resolution classically is to decrease the physical wavelength of the light used in the etching process.
This can come at a tremendous commercial expense. Optical sources and imaging elements are not readily available at very short wavelengths, such as hard UV or soft x ray.
The present system uses a plurality of entangled particles, e.g., photons, in a lithographic system to change the lithographic effect of the photons.
The multiple entangled photons can etch features whose size is similar to that which could only be achieved by using light having a wavelength that is a small fraction of the actual light wavelength that is used.
In one disclosed embodiment, two entangled photons can be used to form an interference pattern that is double the frequency, or half the size, of the actual optical frequency that is used. This operation goes against the established teaching and understanding in the art that the wavelength of the illuminating light forms a limit on the size of features that can be etched. Usually, these features could not be made smaller than one-quarter or one-half of the wavelength of the light used to carry out the etching.
The present system enables forming features that are smaller than one-quarter of the wavelength of the light that is used, by some multiple related to the number of entangled particles that are used.
The present system for quantum lithography uses an interferometer that forms an interference pattern whose fringe spacing depends on both the number of entangled photons entering the device as well as their wavelength. Multiple entangled photons are used within the interferometer. These n entangled photons experience a phase shift that is greater, by a factor of n, than the normal phase shift that would be experienced by a single photon of the same wavelength in the same device. The changed phase shift forms a changed interference pattern in the output to achieve a changed frequency of interference fringes. By so doing, finer features can be etched.
An n-fold improvement in linear resolution is obtained by using n entangled particles, e.g. photons. A two dimensional lithographic operation effectively squares the improvement to density (n2). As such, the entangled quantum lithography system makes it possible to etch features, for example, that are 1 to 10 nanometers apart, using radiation that has a wavelength xcex, of 100 nanometers or more.
Another important use of this system is to retrofit an existing system. Interferometric lithography systems are already known and used. This system makes it possible to re-use those existing lithographic systems to obtain better etching results. The established techniques of improving lithographic technology is by requiring owners to buy or build totally new semiconductor fabrication equipment that use shorter wavelength light. This system improves the resolved output of the same equipment. This allows existing interferometric lithography equipment to be effectively retrofitted.
Also, previous attempts to reduce feature size have used shorter wavelength light to reduce the feature size. That shorter wavelength light is always more energetic. Hence it can cause damage to the substrate.
In contrast, the present system reduces the etched feature size without requiring more energetic particles.